Boiler system stabilizing damper and flue control method

ABSTRACT

One embodiment of a boiler system stabilizing damper for boiler flue systems comprising a cylindrical main housing ( 418 ), a pressure sensing means composed of sensor cap ( 414 ) and sensor hole ( 416 ), a pressure loss generating means composed of a single blade damper ( 410 ), a shaft ( 406 ) and motor ( 404 ), and a controller ( 402 ) comprising a pressure transducer and electronic control. Other embodiments are described.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of provisional patent applicationSer. No. 61/338,727, filed 2010 Feb. 23 by the present inventor.

FEDERALLY SPONSORED RESEARCH

Not Applicable

SEQUENCE LISTING OR PROGRAM

Not Applicable

BACKGROUND

1. Field of Invention

This invention, the stabilizing damper and boiler flue control method,applies to flue gas venting systems, and is used to control andstabilize both the flue venting system and the boiler/heater operations.

2. Prior Art

For purposes of discussion in the remainder of this document, unlessotherwise stated, we will refer to all combustion heating equipment thatincorporates a flue system, as a boiler. The particular type of heatingequipment does not affect the operation of this invention.

This section explores boiler flue venting systems that incorporate oneor more boilers. Current control functions for flue venting systems, andmethods for stabilizing boiler operations via a venting system will beexamined. To illustrate the prior art and its limitations, we begin witha discussion of the overall structure of a boiler system as illustratedin FIG. 1, and the functions of a boiler system as depicted in theschematic representation in FIG. 7. FIG. 1 illustrates a typical exampleof a boiler system comprising three boilers 102 connected in a commonflue architecture that includes a common breach section 108. Thisexample includes barometric dampers 104 on each boiler which is onemethod used with current boiler designs for stabilizing boiler and flueoperations. These barometric dampers are connected between the flueoutlet of the boilers 103 and the riser inlets 105 to the breachsection. The breach section acts as a manifold connecting the multipleboilers to the common chimney 110. This example shows a mechanicalventing system which includes a flue exhaust fan 112, and a breachpressure sensor 106. The part of this entire boiler system originatingfrom the flue outlet of the boilers and ending at either the chimneyoutlet, or the exhaust fan in a mechanical venting system, is the boilerflue system.

The ultimate purpose of a boiler system is to provide building heat,domestic hot water (DHW), or process heat. Except for certain minorcases, there is always a variable demand rather than a constant demandfor the quantity of building heat, DHW heat, and process heat. Asexample, the heat demand in a building will vary depending on theoutdoor temperature. An increase or decrease in the outdoor temperaturewill require a corresponding change in the building heat demand and theheat output of the boiler system. A typical boiler provides heat at aconstant output rate. Because of this, a boiler cannot generate heatthat continuously matches the process or building heat demand. Aconstant output will result in either too little or too much heat. Inorder to match the heat being generated by the boiler system to therequired heat demand of the building or process, a boiler is operatedcyclically as an ON/OFF device over a certain period of time. Oneexception to ON/OFF cycling is the use of a modulating output boiler.The average heat generated over the full cyclic operating period whenthe boiler is ON will equal the total required heat demand over thatperiod. As example, this is a common method employed in a home using athermostatically controlled forced air furnace. When designing a boilersystem, the smallest size boiler is selected that will meet the minimumheat demand without running the boiler in a damaging short cycle. Shortcycling is the excessive switching of a boiler between the ON and OFFstate over relatively short periods of time in an attempt to equal heatdemand. In order to meet the maximum heat demand for the building orprocess, multiple boilers are added until enough heat generatingcapacity is reached to meet that maximum demand. This requiredcontinuous boiler cycling in a multi-boiler system with a common flue isthe root cause of boiler stability problems. Although modulating boilerscircumvent the ON/OFF cycling problem, they still have this stabilityproblem associated with flue venting. It is this stability problem thatneeds to be solved.

There are only two possible ways to connect boilers to a boiler fluesystem. One way is for a single boiler to be connected into its ownindividual boiler flue system. The other way is for multiple boilers tobe connected into a single boiler flue system, referred to as a commonflue configuration. This common flue configuration in combination withboiler cycling is the source of boiler stability problems arising frommulti-boiler systems. Because this is the only way to connect multipleboilers into a single boiler flue system, the stability issue is alwaysinherent to the design. This creates a problem difficult to correctusing current methods. In addition to the stability problem, thisconfiguration tends to reduce boiler efficiency. Although lesscomplicated, stability issues also exist with single boilersincorporating a single flue. In this case, the efficiency problem is theoverriding, one.

The stability and efficiency issues can be understood from the keyfunctional aspects of how a boiler system operates which are illustratedin FIG. 7. FIG. 7 is a schematic representation of the processesinherent to a complete boiler system. These boiler system processes canbe divided into three sub-processes. They are the combustion sub-processCC, the heat transfer sub-process HE, and the draft sub-process FM.Everything begins with the combustion of the fuel/air mixture, whichproduces the hot flue gases that are the ultimate source of heat for theboiler system. This is the first sub-process CC. The hot flue gases thenmove into the heat exchanger, which transfers the heat from the fluegases to a heat transfer medium such as water. A heating system thatuses water as a heat transfer medium is referred to as an hydronicheating system. This heat transfer process constitutes the secondsub-process HE. The extracted heat has many uses such as heating abuilding or providing heat to a manufacturing process. Finally, the fluegases are removed from the boiler(s) and moved into the flue piping,which can include a chimney and/or exhauster fan(s). We call this thirdsub-process the flue mover FM. The flue mover is commonly referred to inthis industry as a flue gas venting system, but for our purposes “fluemover” is more descriptive of its actual function. The flue gases aretransported through the flue mover and are subsequently disposed. Thisis usually into the outside air or atmosphere, but could also be intosome post processing application such as a gas scrubber to removecontaminants or CO₂. The key to making this entire boiler system processoperate correctly and efficiently is the proper control of thevolumetric flow rate of the fuel/air mixture (combustion gases) and fluegases through the boiler itself. The volumetric flow rate of thecombustion and flue gases is ultimately controlled by the flue moversub-process FM. This is why we prefer calling the flue gas ventingsystem a “flue mover”, because that is its exact function. This fluemover is the key to the proper, efficient operation of the entire boilersystem. This flow rate establishes the residence time and pressures ofthe combustion gases in the combustion chamber and the flue gases in theheat exchanger. The residence time and the pressures in the combustionchamber determine the reaction mechanisms and efficiency of thecombustion process. The residence time in the heat exchanger determinesthe efficiency of the heat transfer process from the combustion (flue)gases to the heat transfer medium.

The discharge static pressure at the flue outlet of the boiler is ameasure of the flow rate of the fuel/air mixture and flue gases throughthe boiler equipment (the combustion chamber, and heat exchanger).Measuring this pressure with a magnehelic gage is one technique used toset up a boiler during boiler commissioning, or to diagnose problemsduring operation. In order to move the flue gases from the dischargepoint of the boiler through the flue section (flue mover) and maintainthe correct discharge static pressure, the static pressure throughoutthe flue section must be continuously more negative in the direction offlow from the discharge of the boiler to the discharge of the fluesection (the chimney outlet). The problem with the current design offlue sections which causes the instability problems lies with theinability to maintain the correct static pressures at all times in everylocation throughout the flue system. This occurs as a result of boilercycling.

As previously mentioned, two basic types of flue systems currentlyexist: a single boiler incorporating a single flue, and multiple boilersincorporating a single flue. The flue system may or may not include achimney. There are four possible ways that flue gases can be forcedthrough the flue system. The first is with a chimney and is called anatural draft system. In this case, the required negative pressuresrelative to the discharge point of the boiler are generated by the stackeffect in the flue system. This creates the necessary forces within theflue mover to move the flue gasses and the combustion gases. The secondand third methods involve two types of mechanical draft or mechanicalventing systems. One type of mechanical venting system uses an exhaustfan(s) alone. In this case, the negative flue pressures with respect tothe boiler flue outlet are created by the venting or exhaust fan(s). Thethird type uses an exhaust fan(s) in combination with a chimney. Thisapproach uses a combination of both a fan and the stack effect to createthe negative flue pressure in relation to the boiler discharge point.The fourth method involves the use of a fan assist within the boileritself to force the combustion and flue gases through the boiler. Thismethod is commonly used with category III and IV (positive pressure)flue movers. This fourth method creates a new problem in multi-boilersystems in maintaining the correct, required, negative pressure gradientwithin the flue mover. All flue movers must use a negative relativepressure gradient through the flue system to provide the correct drivingforce for moving the flue gases.

There are several methods currently used to control flue gas flow ratesin the flue mover as operating conditions change within the system. Fornatural draft systems this is normally done with a barometric damper.This works by pulling in cooler room air and mixing it with the hot fluegases, thus cooling those flue gases and increasing their density, whichin turn reduces the stack effect. The result is a reduction in the fluegas flow rate. The assumption for this method to work is that an excessstack effect always exists within the flue system. The barometric damperworks in a Category I, or non-condensing negative pressure, flue systemonly. This technique will not work with high efficiency boilers and lowNOX positive pressure boilers. The excess heat in the flue gases, plusthe use of indoor air to cool the flue gases is a source of inefficiencyfor this type of system. Natural draft systems can also incorporate adraft hood to initiate the flow of flue gases when the boiler firstturns on. If a chimney does not contain hot, low density, flue gases,there will be no stack effect to create flue gas movement. A draft hoodworks by starting the process of filling the chimney with hot flue gasesthus creating the stack effect. As with the barometric damper, thiscreates boiler inefficiency. Another method for initiating the stackeffect is to use a two stage or multistage boiler firing system. Thefirst stage, or low fire stage, provides a means for slowly filling achimney with hot flue gases in order to start the natural draft process.Another method currently used to control boiler flue gas flow rates,which applies to mechanical draft systems, uses a variable speed fan tomove the flue gases. A single pressure sensor in the main breach is usedfor controlling fan speed in an attempt to regulate breach pressures.This works by varying the fan speed in order to hold at least onesection of the main breach at a pressure set point. The problem withthis approach is that it does not control the required pressure gradientthroughout the flue system. This in turn fails to control the allimportant pressures in the boiler branch sections of the flue systemduring boiler cycling. The net effect is boiler system instability.Another method used in an attempt to control boiler instability is toincrease the breach diameter. This tends to reduce the effects of boilerinstability to a tolerable level, but does not eliminate it. In additionto failing to eliminate instability, there are restrictions imposed onboiler layouts using this method. This limits boiler system designoptions and results in increased building costs.

An improper flow rate, or a flow rate of flue gases that is not withinspecifications, is referred to as an uncontrolled draft. An uncontrolleddraft results in flue gas flow rates being higher or lower thanspecifications. An uncontrolled draft can be in either a fixed orconstantly fluctuating state between too high and too low. Anuncontrolled draft that is too high is an overdraft case. Anuncontrolled draft that is too low is an under draft case. A controlleddraft is often referred to as a balanced draft, and this is the fluestate that is desired for the proper operation of the boilers.

The following are some of the consequences of uncontrolled draft:

-   -   1. Poor combustion efficiency.    -   2. Unstable pilot.    -   3. Pilot and main flame ignition problems.    -   4. Flame retention and flame failure problems.    -   5. Unstable flame pulsations.    -   6. Incorrect fuel/air ratios that result in problems such as        sooting, CO and NOx.    -   7. Heat transfer problems within the heat exchanger.    -   8. Incomplete combustion carried into the breach piping.    -   9. Damage to the boiler/heating unit, and/or the flue piping.

An actual case history illustrates the substantial problems that existusing the current flue control methods. FIG. 2 shows a boiler layoutemployed in a boiler heating system. It consists of four boilers in acommon flue architecture with a chimney and employing mechanical draftexhausters. By definition, a boiler system firing state is one of thepossible combinations of ON OFF conditions for each and every boilermaking up a boiler system at some point in time. For example,considering the boiler system in FIG. 2, one firing state would beboiler #1 ON and all others OFF at a point in time. Another state wouldbe Boiler #2 ON and all others OFF at a point in time. The full gamut offiring states would be all possible combinations of ON OFF states forthe boilers in the system.

FIG. 3 is a table showing operating data for some of the boileroperating states for the example boiler system illustrated in FIG. 2.Each column in this table gives the operating data for one of the fourboilers, labeled 1 through 4 in a particular boiler system firing state.The table shows four columns, one for each boiler. Each row, labeled 1through 7, is the full operating data for the boilers during a firingstate at a point in time. This data consists of the ON/OFF state of theboiler with the boiler discharge pressure below measured in inches ofwater column (InWC). The required boiler discharge pressure, asestablished by the manufacturer of the boilers in this system, was inthe range from −0.05 InWC to 0.0 InWC.

For a stable system, the boiler discharge pressure must be within therecommended operating range as established by the boiler manufacturerfor all possible boiler firing states of the boiler system. As shown bythe data in this table, the magnitudes of the boiler discharge pressuresin this system range widely from 0.0 InWC to −0.6290 InWC depending onthe firing state of the boilers. The extremely high negative pressuresare well out of the acceptable operating limits, in some cases by over afactor of ten. Furthermore, as the boiler system changes from one boilerfiring state to another, the boiler discharge pressures fluctuate wildlyoutside the recommended operating pressures as established by themanufacturer. This is a classic example of a seriously unstable boilersystem, and is not uncommon in the industry. The remedies for such aproblem are typically very expensive. This expense is compounded by thefact that these types of instability problems do not normally show upuntil the system has been fully installed and is in the process of beingcommissioned. Often, the end result is to completely replace the systemusing a trial and error approach to find some workable solution. Manytimes, if the system instability does not create a situation that is toofar out of tolerance, the system is left as is. This often results inpremature failure of equipment, and operating inefficiency.

Current attempts to solve the balance and instability problems consistof using fixed position dampers, barometric dampers, redesigning theboiler system and building to employ multiple single boiler/single fluesystems, and increasing the diameter of the breach piping. The best onecan do with these techniques is minimize the problem, but at additionalcosts. Fixed position dampers usually don't work. A barometric doesn'twork with high efficiency heating units and decreases the efficiency ofless efficient units. Increasing the breach pipe diameter adds costs andhas size limitations without actually eliminating the stability problem.This is the most common approach. An increase in the breach diameternecessitates an increase in the chimney diameter. A common method usedtoday for a mechanical drafting system employs a pressure sensor tocontrol draft. Some boilers incorporate a non-modulating damper that isused to retain the residual heat of the boiler in its OFF state. Whenthe boiler is ON, the damper is fully open. When the boiler is OFF, itis closed to prevent heat from being naturally drafted out the chimneyand thus wasted to the outside. This does nothing to eliminate thestability problem. In a nutshell, the way this is currently handled isto simply find an acceptable way to live with the problem.

SUMMARY

In accordance with one embodiment a stabilizing damper comprises a maintube for housing the unit and providing a means for conducting fluegases through the damper, and incorporating a means located on thedamper inlet end for connecting to the boiler flue output point, andanother means located on the damper outlet end for connecting to theriser inlet to the breach section of the flue system, also incorporatinga pressure sensing cap with a sensor hole in the main tube on thestabilizing damper inlet side for determining the boiler dischargepressure, and incorporating on the outlet side a damper mechanismcapable of varying a damper blade angle resulting in a continuous changein static pressure loss in the flue gas flow of the main tube, a motorfor varying the blade angle or position, and a main controller forinterfacing to the boilers, and controlling the operation of thestabilizing damper.

DRAWINGS Figures

FIG. 1 shows a standard layout for a three boiler flue system withbarometric dampers.

FIG. 2 shows a layout for the example boiler heating system includingthe boilers, the breach and a partial chimney section.

FIG. 3 shows boiler operating state data for the boiler systemillustrated in FIG. 2.

FIG. 4A shows a side view of the stabilizing damper.

FIG. 4B shows an inlet view of the stabilizing damper.

FIG. 4C shows an outlet view of the stabilizing damper.

FIG. 5 shows a perspective 3D view of the stabilizing damper.

FIG. 6 shows a flow chart for the control operation of the stabilizingdamper.

FIG. 7 shows a functional diagram for a boiler flue system.

FIG. 8 shows a layout for a three boiler flue system with thestabilizing dampers.

DRAWINGS Reference Numerals

-   -   102 Boiler    -   103 Boiler flue outlet or discharge point    -   104 Barometric damper    -   105 Riser inlet to breach section    -   106 Breach pressure sensor    -   108 Breach section of boiler flue system    -   110 Chimney section of boiler flue system    -   112 Flue exhauster fan    -   402 Controller for the stabilizing damper    -   404 Damper blade motor for stabilizing damper    -   406 Blade shaft    -   408 Standoff support    -   410 Damper blade    -   412 Pressure sensor tubing    -   414 Pressure sensor cap on main housing    -   416 Pressure sensor hole in main housing    -   418 Main housing    -   420 Stabilizing damper inlet    -   422 Stabilizing damper outlet    -   424 Damper shaft seal bushing    -   426 Sensor cap tube fitting    -   428 Mounting plate    -   CC Combustion sub-process of boiler system    -   HE Heat transfer sub-process of boiler system    -   FM Draft sub-process of boiler system (flue mover)    -   802 Boiler    -   803 Boiler flue outlet or discharge point    -   804 Stabilizing damper    -   806 Breach pressure sensor    -   808 Breach section    -   810 Chimney section    -   812 Flue exhauster fan

DETAILED DESCRIPTION FIGS. 4A, 4B, 4C, and 5—Preferred Embodiment

One embodiment of the stabilizing damper is illustrated in FIG. 4A (sideview), FIG. 4B (bottom view), FIG. 4C (top view), and the isometric viewin FIG. 5. FIG. 5 illustrates the mechanical mechanism of thisembodiment, while FIG. 4A and FIG. 4C also include the controlcomponents. The stabilizing damper has a tubular main housing 418 madefrom uniform sheet material. In this embodiment the main housing is arolled cylinder of constant diameter along the main length of thecylinder. This sheet material can be a metal such as galvanized steel,stainless steel, etc., the choice of which depends on the environment inwhich the stabilizing damper will be employed. A stainless steel such asAL29-4c is preferable in hot, acidic environments to avoid corrosionproblems. Other types of stainless steel or galvanized steel can be usedin more tolerable environments. In a cool, condensing, acidicenvironment a plastic material could be employed provided it wasresistant to attack by the acidic environment, and had sufficientstructural strength for the application. It is preferred that thestabilizing damper inlet 420 be shaped as a standard female opening tofacilitate connection to the boiler discharge piping. It is preferredthat the stabilizing damper outlet 422 be shaped as a standard maleopening to facilitate connection to the riser inlet of the flue piping.

One embodiment of the damper mechanism is a damper blade 410, as a flatcircular plate, attached to a round shaft 406. Other damper mechanismscould be a multi-blade butterfly or an iris. The material choices forconstruction of the damper blade and the shaft would follow the samereasoning as that applied to materials for the main housing. Dampershaft bushings 424 on each end of the damper blade are used forproviding a seal between the shaft and the housing, and to provide asmooth rotation of the shaft and blade. The shaft is connected to amotor 404 which acts as a means for rotating the damper blade. Oneembodiment uses a stepper motor to provide an accurate positioningcontrol of the damper blade. A brushless DC motor is an example ofanother type of motor that can provide positioning control. A mountingplate 428 provides a means of support for the motor mechanism and thecontroller 402, and provides shielding from the potentially hot surfaceof the main tubular section. Standoff supports 408 are attached to themain housing and the mounting plate 428, and provides a means of supportfor the mounting plate. In this embodiment the standoff supports wereconstructed from as thin a piece of sheet metal as mechanically andstructurally possible. Since the outlet flue gases can reach hightemperatures, sometimes on the order of 650 degrees Fahrenheit, a meansis required to protect the electronic controls and motor from excessiveheating. The thin material and cutaway sections for the standoffsupports eliminate overheating from heat transfer by minimizing thecross sectional area needed for significant heat transfer to take place.The small cross sectional area of the standoff support limits heattransfer to the mounting plate, and a large surface area provides adissipative heat transfer path to the surroundings rather thantransmission to the mounting plate. In this embodiment all of thelongitudinal edges were folded to increase the structural strength ofthe standoff support while minimizing the thickness of the constructionmaterial.

A pressure sensing cap 414 is located at the inlet side of thestabilizing damper. For this embodiment, the pressure sensing cap isplaced above the damper inlet approximately a length equal to one radiusof the main housing diameter. The cap and its position provide a stablestatic pressure reading from which the damper operates. In order to keepa stable flue gas flow field, and thus a stable static pressure reading,the pressure sensing cap is kept a length of at least 2 main tubediameters away from the fully open inside edge position of the damperblade. The sensing cap for this embodiment is approximately 2 inches by2 inches in the base dimensions, and approximately 1.5 inches in height.A pressure sensor hole 416 of approximately ¾ inch in diameter for thisembodiment is centered under the pressure sensing cap, and into andthrough the main housing. A sensor cap tube fitting 426 is placed in theside of the pressure sensing cap centered at approximately ½ inch fromthe top of the cap. A pressure sensor tubing 412 is attached to thesensor cap tube fitting and runs to a pressure sensing means which ispart of the controller 402 for the stabilizing damper. This pressuresensor tubing can be made of a flexible material such as rubber tubing,or a rigid material such as stainless steel metal tubing. Theappropriate sensor cap tube fitting is used depending on the type ofpressure sensor tubing used. A controller for the stabilizing damperwould include a means for sensing the pressure at the pressure sensingcap and then activating the motor to move the damper mechanism.

Operation—FIGS. 4A, 4B, 4C, 6, and 8

FIG. 8 shows the system in FIG. 1 with the barometric dampers 104replaced by the stabilizing dampers 804 of this invention. Each of thestabilizing dampers controls the discharge pressure at each of theboiler discharge points 803 in order to hold these pressures at theirrequired operating points.

To stabilize the boiler system and provide flue control, the volumetricflow rate of the flue gases from the boiler needs to be controlledwithin specifications established by the boiler manufacturer. This canbe accomplished by adjusting or controlling three variables at theboiler discharge point: the flue gas velocity pressure, the staticpressure, and the flue gas density.

The main housing acts as a pipe for the transport of the flue gases, aswell as the support for components of the stabilizing damper. Thediameter of the flue outlet of the boiler at the boiler discharge pointis set by the boiler manufacturer from the boiler design specifications.These specifications would include the flue gas density and volumetricflow rate. The volumetric flow rate at any point is determined by theflue gas density, the flue gas velocity pressure and the static pressureat that discharge point. The flue gas density within the stabilizingdamper is the same as that set by boiler specifications. If the diameterof the stabilizing damper is the same as the diameter of the boilerdischarge, the velocity pressure at the pressure sensor hole 416 will bethe same as that set by the boiler specifications. In this case, thestatic pressure measured at the pressure sensor hole is the onlyremaining variable needed to control the volumetric flow rate of theflue gases. The set point static pressure is used for controlling thevolumetric flow rate and is measured at the pressure sensor hole. It isalso the same static pressure as that at the boiler discharge point andset by the boiler specifications. The stabilizing damper controls thisstatic pressure by varying the position of the damper mechanism as theflow conditions vary in the flue system. This in turn controls the flueand stabilizes the boiler system irrespective of the fluctuations inflow properties within the flue system itself.

If the diameter of the balancing damper is different from that of theboiler discharge point, it will be necessary to calculate or measure anew static pressure set point and velocity pressure in order to maintainthe correct volumetric flow rate for the flue gases. Calculating the newstatic pressure and velocity pressure is within the ability of personsskilled in the discipline of fluid mechanics. Instead of calculating thepressure set point, a method for measuring this pressure, after thedamper system has been installed, is presented here. When a stabilizingdamper with a diameter different from the diameter at the boilerdischarge point is installed, it will be necessary to attach a shortsection of straight pipe, typically one pipe diameter in length, at thedischarge point of the boiler followed by either a pipe reducer ordiffuser finally followed by the stabilizing damper. A small hole isplaced into the short section of pipe at the discharge of the boiler,and a magnehilic is used to measure the static pressure at this point.This is a standard technique currently practiced by boiler installers. Asecond magnehelic would be attached to the pressure sensing tube fromthe pressure sensing cap of the stabilizing damper. With the stabilizingdamper maintained open, in the full unrestricted flow position, theboilers are fired and adjusted to the correct operating point using themagnehelic pressure at the discharge of the boiler as a reference. Themagnehelic pressure measured at the stabilizing damper would then givethe correct set point operating pressure for the stabilizing damper.

The damper mechanism creates a varying resistance, and thus a varyingpressure loss in the flow of flue gases, as the damper mechanism changesposition. In this embodiment the damper mechanism is a simple singleblade damper, and a change in the blade angle would constitute a changein position of the damper mechanism. The pressure loss created by thedamper mechanism is equal to the static pressure at the outlet of thestabilizing damper less the static pressure at the pressure sensor hole.Thus, the static pressure at the pressure sensor hole can be heldconstant by a simple adjustment of the damper mechanism as the staticpressure at the outlet of the stabilizing damper fluctuates. Thesefluctuations are a result of variations in the operating conditions inthe flue system, which manifest as instability.

Any flue system will require a means for moving the flue gases thoughthe system. This means has been previously described as the stack effectand/or mechanical venting. All flue systems, whether with thestabilizing damper or not, require a sufficiently more negative staticpressure through the flue system, which is provided by the flue movingmeans. This normally required flue moving means also provides the morenegative pressure at the outlet of the stabilizing damper that enablesthe damper to work correctly.

The controller requires a control signal used to adjust the dampermechanism that controls the discharge pressure of the boiler. Thecontrol signal is supplied through a pressure sensing port made up ofthe sensor hole in the main housing plus the sensor cap, which isattached to a pressure transducer that provides the pressure signal usedby a controller to adjust the damper mechanism. The pressure signal isconstantly monitored by the controller. If the pressure is too low ortoo high, the damper mechanism is adjusted to a more closed or more openposition, creating more or less static pressure losses from the dampermechanism until the boiler discharge pressure is within the properoperating range for the boiler. Electronic control means and controllersare readily available for this control purpose. A wireless controller isideal for this purpose. An example of a control strategy for thisinvention that can be incorporated within an electronic controller isshown in the flow chart in FIG. 6.

As the pressures within the flue section fluctuate from variations inboiler firing cycles and atmospheric changes, creating conditions forinstability and inefficiency in the boiler system, the stabilizingdamper holds the boiler discharge pressure within its proper, optimaloperating range.

Advantages

From the description above, a number of advantages of some embodimentsof the stabilizing damper become evident:

-   -   (a) First and foremost, this damper provides a means to        eliminate the system instability problems currently associated        with boiler room flue system.    -   (b) The stabilizing damper affords a significant reduction in        design, material and installation costs for boiler systems.    -   (c) The stabilizing damper provides a means for improving the        efficiency of boiler operations.    -   (d) The stabilizing damper simplifies boiler system design        methods and is more forgiving of boiler system design errors.    -   (e) The stabilizing damper will permit Category I II III and IV        boilers to be installed in a Category I breach flue system. This        is impossible by current methods.    -   (f) The stabilizing damper will permit the mixing of Category I        II III and IV boilers in a common flue system. This is        impossible by current methods.

Conclusion, Ramifications, and Scope

Accordingly, the reader will see that the stabilizing damper of thevarious embodiments solves the current boiler instability problems thatplague this industry. Furthermore, along with the stabilization ofboiler operations comes an improvement in the efficiency of boileroperations. Another unexpected result of the stabilizing damper is thepotential for reduced design and installation costs for the boilersystem, and also potential reduced costs for the building itself. Theuse of the stabilizing damper provides for a boiler design that is farmore forgiving of design errors.

Although the description above contains many specificities, these shouldnot be construed as limiting the scope of the embodiment but as merelyproviding illustrations of some of the presently preferred embodiments.For example, the main housing although presented as a cylindricaldevice, could be of another shape such as a square, oval, etc.; thecontroller can be a wireless electronic device rather than the usualwired controller.

Thus, the scope of the embodiment should be determined by the appendedclaims and their legal equivalents, rather than by the examples given.

1. A stabilizing damper for flue control and boiler system stability,comprising: a.) a fluid conduit enabling the transmission of a gaseousfluid, b.) a means near the inlet of said fluid conduit for sensing thestatic pressure of said gaseous fluid, c.) a means near the outlet ofsaid fluid conduit for generating a variable pressure loss in saidgaseous fluid, and d.) a controller in communication with said staticpressure sensing means, and in communication with said means forgenerating a variable pressure loss, the controller comprisingelectronic circuitry capable of controlling said variable pressure loss.2. The stabilizing damper of claim 1 wherein said conduit is ofcylindrical geometry.
 3. The stabilizing damper of claim 1 wherein saidconduit is of oval geometry.
 4. The stabilizing damper of claim 1wherein said conduit is of rectangular geometry.
 5. The stabilizingdamper of claim 1 wherein said sensing means is a hole through saidconduit and covered by a rectangular is of cylindrical geometry.
 6. Thestabilizing damper of claim 1 wherein said pressure loss means is asingle blade damper.
 7. The stabilizing damper of claim 1 wherein saidpressure loss means is a butterfly damper.
 8. The stabilizing damper ofclaim 1 wherein said pressure loss means is an iris damper.
 9. Thestabilizing damper of claim 1 wherein said controlling means comprises astepper motor, a pressure transducer and an electronic control.
 10. Thestabilizing damper of claim 1 wherein said controlling means comprises abrushless DC motor, a pressure transducer and an electronic control.